The present invention relates to a protective device for use in bicycles, and more particularly to an improvement in the device to be incorporated in a rear derailleur of bicycles for preventing a drive chain from being disengaged with the smallest sprocket wheel of a multi-stage free wheel assembly.
In a multi-speed type of bicycle equipped with a multi-stage free wheel assembly externally installed on one end of a rear wheel spindle and a rear derailleur cooperatively connected to said free wheel assembly, it is well known in the field that a running chain is inclined to be unexpectedly disengaged from the smallest sprocket wheel (top gear) of the free wheel assembly when the chain is shifted from a lower gear to the top gear, viz. from a larger sprocket wheel to the smallest one under the swing function of the rear derailleur. In case the drive chain is unexpectedly disengaged during cycling, it, as a matter of course, causes interference with or stopping the cycling and sometimes may happen to bring about a serious accident.
In avoiding this deficiency, it has been apparent to those skilled in the art that provision of a proper protective device in place near the outward surface of the smallest sprocket wheel is effective. Nevertheless, most of conventional bicycles were not equipped with such protective device. However, several kinds of such protective devices including a finger type, a nail type, a hook type and the like have recently been proposed. And among them, some are proposed in the form of a separately-made part to be fixedly secured to a suitable position of a shifter body or its vicinity of the rear derailleur by means of one or more mounting screws, while others are proposed in the form of an integral part which offsets from a certain portion of the shifter body, a pulley cage or the like of the derailleur. However, such conventional protective devices are designed for only use in a specific derailleur of one manufacturer and cannot be applicable to a derailleur provided by other manufacturers. Therefore, the conventional protective devices are not available to those bicycles which have been delivered to users without any protective device. Further, since some of the conventional devices are rather intricate in configuration, it is not always easy to incorporate with the rear derailleur during manufacturing process, and position adjustment is usually required so that a chain fall restricting surface of the device may face effectively in one direction because those devices are not synmetrical in configuration. Still further, most of the conventional devices are not always easy to manufacture and do not permit a very low expense owing to a specific configuration thereof. Yet further, the conventional protective devices are not easy to exchange when they are broken or damaged.
The present invention contemplates over known types of the protective devices. According to the present invention, the protective device is formed to be of most simple configuration, wherein a cylindrical portion and a substantially flat flange portion extending integrally from one end of said cylindrical portion are provided, said cylindrical portion being internally threaded so as to be screwable, in place of a known lock nut, onto a mounting bolt which is inserted through a shifter body and a hook-shaped bracket, both known elements of the conventional rear derailleur, and the smooth outer surface of said flange portion being designed to perform a desired prevention of the drive chain from disengagement with the smallest sprocket wheel. The protective device according to the present invention is employed in place of a mounting nut which has been conventionally screwed on said mounting bolt for locking the shifter body to the hook-shaped bracket together. In other words, the protective device according to the present invention performs a mounting function as well as a chain fall preventing function, and therefore, the mounting nut which has been hithertofore required is no longer necessary.
Therefore, it is an object of the present invention is to provide the simplest type of protective device for preventing a drive chain from being disengaged from the smallest sprocket wheel.
Another object of the invention is to provide an improved protective device which can be easily incorporated with most of known type rear derailleurs.
A further object of the invention is to provide an improved protective device which permits a very low manufacturing cost.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of some of the preferred embodiments thereof taken in conjunction with the accompanying drawing.